Polypropylene has a variety of properties desirable in a number of applications such as nonwoven fabrics, fibers, films and injection molded articles, including stiffness, toughness, chemical resistance, and heat resistance. Copolymerizing α-olefins with propylene and blending polypropylene with copolymers have broadened polypropylene applications where polypropylene homopolymers were limited by poor physical properties such as impact resistance or toughness.
The goal to decrease stiffness and gain flexibility or softness is hindered by the inherently lower crystallinity and slow crystallization of the copolymer or blends of isotactic polypropylene (iPP) with amorphous elastomers. Nucleating agents increase the rate at which nucleation events occur, often enabling significant crystallization at temperatures higher than possible in the absence of such an agent. However, the addition of conventional nucleating agents to shorten processing times has also generally increased crystallinity and thus increased the stiffness of the polymer article. There is a need for a nucleating agent that enhances the crystallization rate of a propylene based polymer with minimal if any change of crystallinity and the properties governed by crystallinity, such as, for example, modulus and impact resistance.
U.S. Pat. No. 6,747,114 describes an adhesive composition that can include a semi-crystalline, preferably random, copolymer of propylene and at least one comonomer selected from the group consisting of ethylene and at least one C4 to C20 α-olefin.
U.S. Pat. No. 6,635,715 describes thermoplastic polymer blend compositions comprising an isotactic polypropylene component and an α-olefin/propylene copolymer component, said copolymer comprising crystallizable α-olefin sequences.
Other background references include US 2007/0240605 (also published as EP 1778781 and WO 06020309), U.S. Pat. No. 4,645,792; U.S. Pat. No. 4,749,736; Bourland, Polymer Preprints (American Chemical Society, Division of Polymer Chemistry) 28(2), 385-7 (1987); Bourland, Plastics Engineering (Brookfield, Conn., United States), 43(7), 39-41 (1987); Pospisil, Journal of Materials Science Letters, 9(4), 495-6 (1990); Janimak, Polymer Bulletin (Berlin, Germany), 22(1), 95-101 (1989).